This scientific report describes the effect of feeding detoxified karanj seed cake as protein replacement of soya bean meal on immunity and pathology in growing lambs. Twenty-four male lambs, 4-6 months of age were divided into four groups of six each and fed with different levels of detoxified karanj seed cake (dKC 0%, dKC 25%, dKC 50%, dKC 75%) for 140 days. Effect on humoral and cell mediated immunity was assessed by antibody titer against Peste des petites ruminants (PPR) vaccination and lymphocyte proliferation assay, respectively. Significant decrease in the humoral immunity in high dose fed group and no change in stimulation index of lymphocytes in all the groups were observed. On histopathology, dKC 75 showed severe changes in intestine, testis and mesenteric lymph node. Thus, the present process of detoxification of karanj seed cake is useful for feeding growing lambs up to 50% protein replacement levels, with little adverse effect on immunity and pathology.